In embodiments, a WCD system includes electrodes (304, 306, 307, 308) with which it senses ECG signals (311, 312, 313, 314, 315, 316) of a patient (82). A processor (230, 330) may detect sequential peaks (621, 622, 623, 624, 625, 626, 627, 628, 629) within one of the ECG signals, measure durations of time intervals (651, 652, 653, 654, 655) between the peaks, including between non-sequential peaks, and identify a representative duration (881, 981, 1081, 1181) that best meets a plausibility criterion. The plausibility criterion may be that the representative duration is the one that occurs the most often, i.e. is the mode. Then a heart rate (333) can be computed from a duration indicated by the representative duration (881, 981, 1081, 1181) and, if the heart rate (333) meets a shock condition, the WCD system may deliver a shock (111) to the patient (82). An advantage can be that the representative duration (881, 981, 1081, 1181) can be close to a good R-R interval measurement of the patient (82), notwithstanding noise in the ECG signal that is in the shape of peaks (531, 532).
